Lipids as currency in ecological interactions: Competition and facilitation between two lipid scavenging parasitoids

Abstract

AbstractInterspecific interactions in nature often revolve around the acquisition of nutrients. Depending on the organisms’ metabolic requirements, competition for specific essential nutrients may occur, which selects for increased abilities to monopolize, consume and store these nutrients. Lipid scavengers are organisms that rely on exogenous lipid acquisition as they lack the ability to synthesize fatty acidsde novoor in sufficient quantity. Most parasitoid insects are lipid scavengers: they obtain all required lipids by feeding on their hosts as larvae. Here we study the nutritional ecology of competitive interactions between nativeNasonia vitripennisand introducedTachinaephagus zealandicus. While the former was already known to lack lipogenesis, we show thatT. zealandicusalso relies on host lipids. The interactions between the two species were studied using competition experiments, in which oviposition ofT. zealandicuson a host was followed by multiparasitism byN. vitripennis. The outcome of competition was determined by the duration of the time lag between oviposition events.N. vitripenniswas superior when arriving 3 days after oviposition byT. zealandicus. In contrast, 9 days after oviposition ofT. zealandicuswe observed complete reversal, and noN. vitripennisoffspring were able to develop. Only whenN. vitripennislaid eggs 15 days afterT. zealandicusoviposition, both species could emerge from the same host. However,N. vitripennisrealizes only 10% of its potential fitness at this time point because prior parasitization by the gregariousT. zealandicuscompartmentalizes the host resources, limiting the spread ofN. vitripennis’venom. This study shows that successful reproduction ofN. vitripennisat 15 days was achieved by hyperparasitizing, a capability that provides a fitness benefit toN. vitripennis, as it extends the time window that hosts are available for parasitization. Choice tests with hosts at different time intervals afterT. zealandicusoviposition revealed a partial mismatch inN. vitripennisfemales between competition avoidance and offspring performance, which may be linked to the limited co-evolutionary time between native and introduced species. We discuss our results in the context of nutritional ecology and, specifically, the role of lipids in ecological interactions.